Labster Logo

Time of Flight (TOF)

The MALDI ionization method is coupled with a mass analyzer called time-of-flight (TOF). In TOF, the time ions take to reach the detector is measured. The velocity is determined by the mass-to-charge ratio (m/z). Smaller ions will reach the detector before large ones due to the fact they have less mass. The charge of the ions also determines the velocity. Ions with 2 or more positive charges will move faster than ions with only 1 positive charge. Thus, those ions that are both smaller and positively charged will move faster. However, keep in mind that non-charged fragments, like radicals, won't be detected by the instrument.

The output of the detector is the mass spectrum, displayed in a “stick diagram”. This shows the relative current produced by ions of varying mass/charge ratios.

This is an overview of a mass spectrometer. The shape of it looks like a big vertical rectangle with a small base and a squared tip, similar to a giant battery. The squared tip is where one of the detectors is located. Below it, a small rectangle forms the retractailer post-acceleration detector and seven long rectangles form the reflectron. The base of the spectrometer is where the optical sensor and the X Y camilestage. Right above them, the target plate is placed. The laser is outside the big rectangle structure and its beam points directly to the sample with the help of three lenses, two of which are also outside the spectrometer. The sample, depicted as two big arrows, after being hit by the laser, hits the afore-mentioned detector and bounce to a second detector found in the middle and left part of the spectrometer.

Figure 1. View of the Mass Spectrometer´s Composition

Referred from:

Article
Mass Spectrometry